JPS5925219B2 - copying device - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION Conventional contact fusing devices are known as an effective, compact and flexible means for fusing thermoplastic powder images to support sheets.

By using superior design techniques that pay special attention to heat transfer and material selection, contact fusing devices fuse and support thermoplastic images without being adhesively attached to a support sheet. It can be configured to press against the seat. Adhesion of toner to the adhesive surface of the fusing device disturbs the next copy,
In severe cases, the copy sheet may stick to the surface of the fusing device, resulting in a paper jam. It has been found that a maximum tendency for adhesion between the copy being fused and the heated fuser roll of a contact fusing device exists when large area, very dense images are being fused. . This adhesion tendency problem is greatest adjacent to the leading edge of the copy sheet where the copy sheet must begin to peel off from the heated fuser roll due to the large area of high image power. In the reproduction of ordinary documents, such as letters, diagrams, and photographs, it is unusual for there to be large areas of solid black, usually at one end of the original.

When a copy image is created by being exposed to light reflected from the original document, the absence of a document to reflect the light results in a dark black image over the entire area outside the boundaries of the document. It's going to happen. For this reason, typical reflective copiers are equipped with a document cover that creates a white background superimposed on the document that is smaller than the exposure window. However, the superimposed white backing is ineffective when making copies from pages of thick documents, such as books, or when the operator forgets to close the cover. That is, books whose pages are substantially smaller than the copier's exposure window tend to produce copies with at least one solid black edge. If one of these edges is the leading edge of the copy sheet as it passes through the copying process, the potential for paper feed failure in the contact fuser is at its greatest. The inventor has devised an apparatus which operates to sense the average reflected light intensity from the exposure window during exposure window scanning.
A normally operating inter-image erase circuit energizes the erase lamp at the beginning of a copy cycle to prevent development of the photoconductor in certain areas outside the preset image area. During an exposure scan, the control circuit compares the sensed average light intensity to a preset threshold value. If the sensed reflected light exceeds the threshold value, the erase lamp is extinguished and the copying process proceeds normally. The copies made will exhibit good white edges that pass through the contact fusing device easily. Additionally, toner consumption and cleaning requirements are reduced. The invention may be implemented using a variety of techniques different from the embodiments described above.

The image at the tip does not need to be completely erased for the present invention to be effective. That is, by increasing the bias voltage of the magnetic brush in the developer station, it is possible to reduce the density of light in the region of the tip while retaining any information found in the original document that has a dense image near the tip. A statue can be made. The tip image can be brightened or erased by control of the transfer station or, if timing permits, control of the sensitizing charging corona. For average light measurements, the average light intensity is preferably sensed by a light detection device mounted on a member positioned relative to the scanning footprint of the reflected light (FOOtprint), such as a scanning lens. Other devices can be used.

However, only the light reflected from at least a representative sample of a small cross-scan area spanning the document window is
It is important that the photodetector is accessible in such a way as to guarantee an accurate time relationship between threshold detection and the controlled copying process. More expensive and less reliable, an averaging circuit uses multiple photodetectors placed close to the exposure window itself and electrically combines the outputs of all detectors before threshold comparison. It is possible to detect the average light intensity by providing As mentioned above, copiers are typically provided with document covers that have a bright background that avoids the problems to which the present invention is directed.

For copiers that can make copies of thick documents, such as books, a document cover is provided that lifts to accommodate the thickness of the book. Preferably, the practice of the invention includes means for sensing the position of the document to enable edge erasure control only when the document cover is in the raised position. Thin documents with dark images adjacent to the edges can be copied straight to the edge by a machine equipped with the present invention, while automatic edge detection and density control always operate with the document cover open. Performed when a copy is being made. 1, a sensitized charging corona 13, an imagewise exposure station 14, a magnetic brush development station 40 forming a toner powder image 15 on surface 12,
and a photoconductive peripheral surface 12 that is moved along a copy replay path 12a through an electrostatic imaging operating point implemented by a transfer corona station 16 that transfers the powder image 15 to a copy sheet 17. A xerographic type copier or printer is shown including a rotating drum or imaging member 11.

Cleaning station 18 removes residual toner particles from photoconductive surface 12 before it is opposed to sensitized charging corona 13. At exposure station 14, a fragmentary streaming light image reflected from document 19 supported on exposure window 31 by optical scanning device 20 in light-tight housing 30 is directed onto photoconductive surface 12. Passage 1
It can be presented in synchronization with the movement along 2a. This flow image is generated by movement of an optical component, such as lens 21, along scanning path 21a parallel to one axis of exposure window 31. lens 21 is mounted on scanning carriage 22;
It is then supported by suitable rails or tracks 23. Carriage 22 is driven via transmission means 24 at a suitable speed to provide a flow image that is synchronous with drum 11. Flexible diaphragm or curtain member 3
2 surrounds the lens 21 and only light passing through the lens 21 can reach the photoconductive surface 12. A pair of normally stationary mirrors 33 and 34 redirect light received from lens 21 onto photoconductive surface 12.

To maximize light efficiency and to minimize the effects of the curvature of photoconductor surface 12, a narrow segment or footprint 25 of exposure window 31 is projected through lens 21 at a given time.

This is accomplished by a stationary incandescent lamp 35 directing a narrow transverse beam of light through a stationary mirror 36 and a movable mirror 26 to the exposure window 31 so as to illuminate only a narrow footprint 25. Movable mirror 26 has a speed transmitter 24 suitable for scanning the illumination footprint 25 forward through successive segments or image areas of window 31 in optical synchronization with the movement of lens 21 and photoconductive surface 12. A carriage 27 and suitable rails or tracks 28 for movement by
Supported by. The above-described optical device and scanning device are described in the specification of Japanese Patent Application No. 119518/1984 and in the US Patent Application No.
3758774 in detail. A magnetic brush development station 40 applies electrostatic toner powder to the electrostatic latent image formed by exposure station 14.

The development station 40 includes an electrically biased conductive cylinder 4 that functions as a development electrode and can faithfully reproduce halftone and large area solid black images as well as line images.
The magnetic brush unit 42 includes a magnetic brush unit 42 having a magnetic brush unit 42. Powder image 15 formed by developer station 40 is transferred to copy sheet 17 which is presented synchronously with the movement and position of photoconductive surface 12.

Copy paper 17 is conveyed by pneumatic conveyor 50 from transfer station 16 through a contact fusing system for fixing the image, in which the powder image is permanently affixed to the paper. Outlet feed roller 52 feeds the completed copy sheet to outlet pocket 53 so that the copy can be removed. The contact fusing device 51 can be of the type shown in the specification of Japanese Patent Application No. 129830/1983. The fusing device consists of a heated fusing roll 54 having an internal heating source and a heated surface 55 of a deformable silicone elastomer having an inherent low tack with respect to the thermoplastic toner material of the powder image 15. Additionally, fusing device 51 includes an unheated back-up device that brings copy sheet 17 and the powder image thereon into contact with heated surface 55 .
A roll or pressure roll 56 is included. The problem to which the present invention is directed is that the document to be copied is placed over the exposure window 31 in such a way that it leaves an uncovered portion 29 near the edge of the window 31 that is first scanned by the lens 21. It mainly occurs when

The cover 37 for holding the document downward is connected to the exposure window 31
It has a white background surface member 38 which is rotatably mounted adjacent to and which can be placed over a thin document placed over the exposure window 31 to cover an area such as that shown at 29. ing. In other words, the uncovered margin portion 29 of the exposure window 31 is mostly exposed when a document smaller than a predetermined size, such as a page of a small book, is being copied and the cover 37 cannot be closed due to the thickness of the document. Commonly occurring. In the absence of a document or white background material to reflect the light from mirror 26, lens 21 projects very little light onto photoconductive surface 12, resulting in a still highly concentrated image that develops as a large area solid black image. The photoconductive surface 12, which remains charged, will face the development station 40. Without the present invention, this solid black image would be transferred to copy sheet 17 in registration with the leading edge of the sheet. The presence of a large solid black image spanning the leading edge of copy sheet 17 indicated a tendency for it to remain attached to fuser roll surface 55. Failure to properly peel the copy from the fuser roll surface 55 can result in paper jams and require a shutdown of the entire machine 10. Large dark images on copy paper 17 at locations other than the leading edge are not critical. For example, once a properly separated leading edge enters the exit supply roll 52, the copy sheet 17 can be pulled away from the fuser roll surface 55 even if a tendency to stick occurs. A light source may be provided to discharge areas on the photoconductor surface between subsequent image areas to minimize toner consumption and extend the life of the filter device that is part of the cleaning station 18. Conventionally known.

In the present invention, a long discharge or erasing lamp 60 is used.
is located between the exposure station 14 and the development station 40. Typically, this discharge lamp 60 has the well-known function of erasing or discharging the photoconductor in the area following the trailing edge of the first copy and in front of the leading edge of the image area for the next copy. We work to provide the following. As long as the leading and trailing edges of the copy are always presented at the same location on the surface 12 of the drum 11, control of the discharge lamp 60 is provided by drum position sensing devices such as the cam 61 and associated switches 62, 63. can be successfully provided. Cam 61 is configured to close switch 62 when the tip of the image area on photoconductor surface 12 reaches a position in alignment with discharge lamp 60. Switch 63 is closed at the time the trailing edge of the image area on photoconductor surface 12 passes discharge lamp 60. As shown in FIG. 2, latching switch 64 operates switch 63 to operate discharge lamp 60.
respond to the close of. As will be described later, when the switch 65 senses that the cover 37 has been lowered and is placed in the position shown by the dashed line in FIG. 2, the latching switch 64 turns off the discharge lamp 60, rendering it inoperable. in response to the closing of the image area leading edge indicator switch 62. The present invention controls the leading edge density of copies made at transfer station 16 by providing an alternating control to turn off lamp 60.

Preferably, the alternation control in the present invention is performed when the document cover 3
7 is in its open position by cover down sensing switch 65, which is located in the solid line position in FIG. The control system of the present invention includes a delay system or delay circuit which is a measure of the time required for a point on the photoconductive surface 12 at the exposure station 14 to move into alignment with the discharge lamp 60. 66, the reflected light intensity rises above a preset threshold to generate a signal to reset the latching switch 64 and disable the discharge lamp 60. A reflected light intensity sensing device 70 including circuitry 80 for detection is used. That is, cover 37 is in a raised or open position, and thus switch 65
When in the solid line position beginning in FIG. . Light intensity sensing device 70 senses low levels of light as long as mirror 26 projects light through window 31 in areas where the light is not reflected back by document 19.

When the scanning band of light from mirror 26 reaches the left or leading edge of document 19, the light intensity received by sensing device 70 rises rapidly and a signal is issued to delay circuit 66. The lamp 60 has passed the delay period (at this point, the electrostatic image at the left edge of the document 19 has reached the discharge lamp 60).
reach the position. ) remains on to discharge photoconductive surface 12 until ). The expiration of the delay time sends an extinguish signal to latching switch 64, thus extinguishing lamp 60 and the copying process proceeds in the normal manner. The tip of the image area on photoconductive surface 12 is lamp 60.
The developing station 40
No toner material is developed on photoconductive surface 12 by . The image is not transferred to the leading edge of the copy paper 17 at the transfer station 16. The untoned leading edge of the copy is easily passed through the contact fusing device 51. By providing switch 65, it is possible to copy the entire area of a thin document, which may include black areas adjacent to the leading scan area of exposure window 31.

Light intensity sensing device 70 is shown in detail in FIG. The device includes a phototransistor 90 mounted below a light focusing lens 71 on a printed circuit board 72 within a housing 73. The housing 73 is designed to prevent light from directly irradiating the phototransistor 90 from the lamp 35.
Full walls 74 and 75 that restrict light from entering 3.
including. Tapered buttful wall 75 limits the lateral field of view of phototransistor 90 . The field of view should be large enough to obtain a useful display sample of the light reflected from exposure window 31 to identify the presence or absence of a document. The geometry of the illustrated scanning system provides an aperture 76 in the right side wall 77 of the housing 73 to allow the phototransistor 90 to receive reflected light throughout the scanning motion of the lens 21 and mirror 26. A condenser lens 71 is mounted directly above the phototransistor 90 to serve to collect light from a wide area of the exposure window 31. The light collected from a wide area represents an average intensity of a narrow illumination footprint 25 that is particularly suitable for identifying the presence and absence of documents on the exposure window 31. As is well known, incandescent lamps such as those shown at 35 produce a significant amount of infrared light as well as visible light.

A dichroic cold mirror 36 is preferably used to reflect only visible light to the exposure window 31 to minimize the tendency to heat the document 19 above the exposure window 31. The infrared light easily passes through the dichroic mirror 36 and the optical system housing 3
It is reflected around 0. The inner wall 39 of the housing 30 is colored with a matte black material to minimize internal reflections. However, the large amount of infrared light generated by lamp 35 is not completely absorbed. In order to minimize undesirable optical noise effects caused by such infrared light, the Blueti
nt filter 78 was used.

This prevents infrared light from propagating to the phototransistor 90. A threshold detection circuit 80 carried by printed circuit board 72 within housing 73 is shown in FIG.

The detection circuit 80 includes a positive power input section 81 and a negative current input section 82.
and a ground potential input section 83. The positive input is flattened by resistor 84 and capacitor 85 and connected to line 88.
to similar circuit branches 91 and 92 to derive a comparison voltage on lines 93 and 94 which is an input to an operational amplifier 86 connected by a resistor 87, such as a Schmitt trigger, to produce an accurate and rapid output on the applied. Circuit branch 91
are a phototransistor 90 whose operating state is changed in proportion to the applied light intensity, and voltage dividing resistors 91a and 9.
1b, a base resistor 95 and a load resistor 96. Resistor 91b includes a variable potentiometer tap 97 to which the responsive threshold of circuit 80 can be adjusted. A voltage level is induced on line 93 that is a function of the light level intensity applied to phototransistor 90 and the particular setting of threshold adjustment potentiometer tap 97. Branch 9
2 includes voltage divider resistors 92a and 92 in addition to a diode 99 that provides a forward voltage drop that varies with ambient temperature in the same manner as the temperature varying voltage drop across transistor 90.
b and load resistor 98, thus canceling out the effects of ambient temperature on the signals presented to lines 93 and 94. In operation, output line 88 is typically connected to phototransistor 90.
The light received by potentiometer tap 9
As long as it is below the threshold set by 7, it exhibits a positive potential.

As the light level rises towards and above the threshold level, operational amplifier 86
The upper polarity is changed to negative, thus detecting the occurrence of a threshold crossing. Potentiometer taps 97 are adjustable to allow adjustment of specific circuit components, and thus certain settings may be made to take into account the overall room lighting in the immediate environment when installing the machine. Mechanical threshold adjustments are provided. Delay device 66 can be a simple single shot circuit whose time constant is set to correspond to the time it takes for a point on photoconductive surface 12 to pass from exposure station 14 to lamp 60.

Such a device works well for machines with predictable constant speeds. Maximum accuracy can be obtained by providing a displacement emitter that operates synchronously with drum 11 to provide a delay that is directly measured by the movement of photoconductor 12. Although the foregoing has described a specific embodiment of the invention in which a photosensitive phototransistor is carried by a scanning lens and controls an erase lamp to prevent development of a dark edge, the concept of the invention Various modifications are possible without departing from this.

For example, instead of using an erase lamp, development is accomplished by increasing the bias voltage on magnetic brush roll 42 to a level that approaches the charge level on photoconductive surface 12.
It is possible to reduce the density at the leading edge of the copy. Also,
It is possible to selectively control the transfer corona so as not to transfer the darkly toned leading edge of copies made from documents of a predetermined size or less. Furthermore, the photosensitive device may be located at other locations than on the moving optical element. A static photosensitive device may also operate successfully if it is positioned to receive a substantially uniform display sample of reflected light from the illuminated steps of the exposure window 31.

[Brief explanation of the drawing]

1 is a diagram illustrating a xerographic type copier or printer using a tip density control means according to the present invention; FIG. 2 is a logic diagram of the control means of the present invention; and FIG. 3 is a light sensing device used in the present invention. A diagram of the apparatus and FIG. 4 is a diagram of the threshold detection circuitry used in the control logic of FIG. In FIG. 1, 12... photoconductive surface, 13.
... Charged corona, 14 ... Image exposure station, 19 ... Document, 21 ... Lens, 37 ... Document cover 70 ... ...Light intensity sensing device.

Claims (1)

Claims: 1. An imaging member including a photoconductive surface movable along a copy-forming path and small steps of a light image reflected from a material disposed on an exposure window. an electrostatic imaging station comprising means for sequentially scanning successive portions of an electrically conductive surface; a powder image development station comprising electrode means capable of developing an intense solid black image; and a powder image transfer station; a copying apparatus comprising: a station for receiving a copy sheet to which a powder image has been transferred; and an image fixing means having a heated surface for contact fusing the powder image to the copy sheet; density changing means exhibiting an operating state and a non-operating state for changing the density of the powder image transferred to the copy sheet, and producing a lower image density on the copy sheet when operating than when not operating; and means operative to sense the instantaneous average intensity of the step-wise display sample of said reflected light image; The above-mentioned copying apparatus is characterized in that it has means for responding to the detection of a rise of a predetermined threshold value or more.